The long term goals of this research are to understand the factors leading to hemoglobin transition during amphibian metamorphosis. Potential erythropoietic organs will be destroyed in an attempt to establish the origin of stem cells. Bovine serum albumin (BSA) gradients will be used to separate circulating red blood cell (RBCs) and cells obtained from erythropoietic organs in an attempt to establish the stages in tadpole and adult RBC maturation which are most affected by thyroid hormones. Cells separated on the BSA gradient will be cultured in the presence of thyroid hormones in an attempt to mimic the progression of normal metamorphosis. Adult and larval RBCs will be monitored for differences in population of charged transfer RNA (tRNA). Half-life studies of larval and adult RBCs will be performed to probe the selective destruction of larval RBCs which probably occurs at the time of metamorphic climax.